Question

A civil engineer is planning an experiment to compare the levels of biological
oxygen demand (B.O.D.) at three different points in a river. These are just upstream
of a sewage plant, five kilometers downstream, and ten kilometers downstream.
Assume that in each case samples will be taken in the middle of the stream (in
practice samples would likely be taken at several positions across the stream and
averaged). One set of samples will be taken at 6 a.m., another will be taken at 2 p.m.,
and a third will be taken at 10 p.m. The design will block the effect of time of day, as
some interfering factors may be different at different times. However, the interaction
of these interfering factors with location is expected to be negligible.

a) If there is no replication aside from blocking, how many tests are required?
b) List all tests.
c) Specify which set of tests constitute each block.
d) How should the order of tests be determined?

Answer 1

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